The present application relates to a lead sealant film and a non-aqueous electrolyte battery. More particularly, it relates to a lead sealant film for use in sealing an electrode terminal lead and the improvement of a non-aqueous electrolyte battery using the lead sealant film.
In recent years, a variety of portable electronic devices, such as camera-integrated video tape recorders (VTRs), cellular phones, and portable computers, have widely spread, which are reduced in size and weight. As a portable power source for these electronic devices, a battery, particularly a secondary battery, especially a non-aqueous electrolyte secondary battery (so-called lithium-ion battery) is being vigorously studied and developed for obtaining a battery which can be further reduced in thickness or which can be bent.
With respect to the electrolyte for such a battery which is a flexible form, vigorous studies are made on a solid electrolyte, and especially a gel electrolyte, which is a solid electrolyte containing a plasticizer, and a polymer solid electrolyte including a lithium salt dissolved in a polymer have attracted attention.
On the other hand, fully utilizing the merits of the above thin and lightweight battery, various studies are made on a battery of a type such that a battery element is sealed using a plastic film or a so-called laminated film including a plastic film and a metal which are laminated together. In the battery of this type, an important issue is to achieve sealing reliability equivalent to or higher than that of a metal can.
For example, when using an external packaging material composed of a plastic film formed from a resin solely like a known battery (see Japanese Unexamined Patent Application Publication No. 2000-268789 which is herein referred to as “patent document 1”), moisture penetration through resin or volatilization of the electrolyte by entering the battery through resin inevitably occurs. Therefore, the use of the plastic film formed from a resin solely is not suitable for the battery utilizing a solid electrolyte using an organic solvent.
For solving the above issue, the use of, for example, an aluminum laminated pack containing a metallic foil in the external packaging film is effective, but, in this case, another serious issue of the occurrence of short-circuiting arises.
A strip-form electrode terminal is introduced from the heat-sealing interface of the external packaging, and, for example, the edge face of the metallic foil of the external packaging material exposed at the edge face of the outlet for the electrode terminal is bought into contact with the electrode terminal to cause short-circuiting. Alternatively, when heat-sealing is conducted at a temperature and a pressure which exceed the respective appropriate temperature range and pressure range, the surface of the metallic foil exposed due to flow of the resin is bought into contact with the electrode terminal to cause short-circuiting.
For solving these issues, a sealant film having a three-layer structure composed of a heat resistant layer sandwiched between other resin layers has been proposed (see, for example, patent documents 2, 3, 4, and 5).
[Patent document 2] Japanese Unexamined Patent Application Publication No. 2000-268789
[Patent document 3] Japanese Unexamined Patent Application Publication No. 2004-095543
[Patent document 4] Japanese Unexamined Patent Application Publication No. 2002-245988
[Patent document 5] Japanese Unexamined Patent Application Publication No. 2002-216720
However, in the developing technologies described above the patent documents 2, 3, and 4, the melting point of each resin layer is not specified, and the constituent resins are not of the same system, and therefore, when forming a three-layer structure, it is necessary to bond the low melting-point resin (layer) and the high melting-point resin (layer) together using a bonding agent. The bonding agent inevitably experiences heat conditions at least two times, namely, during forming the sealant film and final sealing for the battery, and further the battery is possibly stored in a high-temperature environment, and hence there is apprehension that delamination of the bonding agent due to the electrolyte is caused.
On the other hand, in the battery described in the patent document 5, lamination of resins of the same system by extrusion is disclosed, but a film for use is a film subjected to an electron-beam cross-linked on one side, which leads to increase the cost.